The conventional pendant-type automatic sprinkler head includes a body or frame that has an outlet which is normally enclosed by a valve cap, and the cap is held in the closed position by a releasable lever assembly which includes a thermally responsive element, such as a low-melting-point fusible link or a glass bulb. With a pendant-type sprinkler head, the lever assembly extends downwardly beneath the ceiling of the building, and when the temperature increases to a predetermined level, the thermally responsive element will melt, enabling the water pressure in the line to release the valve cap and discharge the water.
In residential dwellings and commercial buildings, it is often desired to utilize a sprinkler head that is located above the ceiling, so that the operative parts are not exposed to view. With this type of construction, the sprinkler head is concealed within the ceiling by a decorative plate that is mounted flush against the undersurface of the ceiling, so that the operative parts are not visible. U.S. Pat. Nos. 3,633,676, 3,714,898 and 4,015,665 describe concealed sprinkler heads.
A typical concealed sprinkler head includes a cylindrical sleeve or cup, which is positioned around the cast metal frame or body, and a decorative cover plate is attached to the sleeve and encloses the sprinkler head as well as the opening in the ceiling. In normal practice, the sleeve is preassembled in the factory with the frame. At the location of use, the sprinkler head, along with the attached sleeve, is installed with the water pipe line and after installation, the sprinkler head is tested for possible leakage. Because of the presence of the cylindrical sleeve, small leakage at the threaded joint may not be readily visible, with the result that the time required for the pressure testing procedure is substantially increased.
In order to properly position the cover plate of the concealed sprinkler head with respect to a suspended ceiling, the body or frame of the sprinkler head must be installed a precise distance from the lower surface of the ceiling. Concealed sprinkler heads, as used in the past, have had minimum provisions for adjustment, with the result that if the critical distance between the body and the ceiling is not maintained, the cover plate would not be positioned flush with the ceiling, thereby resulting in an unsightly gap.
U.S. Pat. No. 5,072,792 discloses a concealed sprinkler head having a preassembled cover plate unit which is attached to the frame of the sprinkler head after the frame is connected to the water line. The frame includes a pair of arms which extend downwardly from the base of the frame and are joined together at a junction. A valve cap normally encloses the outlet in the frame and a releasable thermally responsive mechanism interconnects the junction and the valve cap. When the thermally responsive mechanism is exposed to a predetermined elevated temperature, the mechanism will release and open the valve cap.
In accordance with the description of the above mentioned patent, after the sprinkler head has been installed with the water line and tested for possible leakage, the preassembled cover plate assembly is installed with the sprinkler head. The cover plate assembly includes a cup-shaped outer shell and a mounting ring or disc is located within the shell. Interposed between the upper end of the shell and the ring is a compression spring. In the pre-assembled unit, the ring is held in position within the shell by the engagement of peripheral projections on the ring with notches in the upper portion of the shell. The lower peripheral edge of the shell is connected via a fusible metal, such as solder, to a cover plate.
To assemble the cover plate unit of the aforementioned patent, the sprinkler head of the unit is slipped upwardly over the frame. with the arms of the frame being received within a central opening in the disc. As the unit is moved upwardly on the frame, flexible tabs on the ring engage a groove in the frame. The sleeve and cover plate are then rotated relative to the ring which brings the projections on the ring into registry with elongated slots in the shell. With the projections in registry with the slots, the force of the spring will then bias the shell and cover plate upwardly relative to the ring thus urging the cover plate into engagement with the undersurface of the ceiling.